This invention relates to a direct cylinder injected, two cycle, internal combustion engine and more particularly to an improved control for such engines.
The advantages afforded by the simplicity of two cycle engines is well recognized. Also, the ability of these engines to produce greater horsepower per displacement than four cycle engines due to their firing every cycle of rotation is acknowledged. However, because of the overlap in the scavenging and exhaust cycles and other factors, environmental concerns are making the use of two cycle engines more difficult.
One way in which the performance of a two cycle engine can be significantly improved and, at the same time, the fuel economy and exhaust emission control can be improved is through the use of direct cylinder fuel injection. With this type of injection system, fuel is injected directly into the combustion chamber for combustion therein. By utilizing direct cylinder injection, it may be possible to obtain stratification of the charge and, accordingly, exhaust emission and fuel economy improvement.
However, the fact that exhaust port is opened during a portion of the intake or scavenging cycle gives rise to the possibility that injected fuel can be swept out of the exhaust port. Therefore, it has generally been the practice to inject the fuel very late in the compression cycle and oftentimes fuel injection begins immediately after the exhaust port is closed and before the piston has reached its top dead center position. Such a practice will ensure that fuel does not pass out of the exhaust port.
However, this early injection of fuel, particularly under lower speed and load conditions gives rise to a very great difficulty in obtaining proper mixing in the combustion chamber. That is, when the fuel is injected late, there is less turbulence and airflow in the combustion chamber. This result in poor mixing and incomplete combustion.
It is, therefore, a principal object of this invention to provide an improved direct injected two cycle engine and operating strategy.
It is a further object of this invention to provide a fuel control arrangement for a direct injected two cycle engine wherein the timing of the fuel injection is governed so as to ensure that fuel will not pass out of the exhaust port but also so that the fuel is well mixed in the combustion chamber before ignition timing.
Because of the more frequent firing pulses of two cycle engines, there is also a cylinder to cylinder effect that is greater with two cycle engines than with four cycle engines. That is, if the exhaust ports of several cylinders are served by a common exhaust manifold, the overlap in the exhaust port timing and the exhaust pulses in the system can give rise to effects in one cylinder caused by the exhaust pulses from another cylinder. At times this is used to obtain improved engine performance through a technique which is sometimes referred to as "exhaust supercharging."
However, this concept also can mean that if each cylinder has this injection timing and duration controlled independently of the others, then the desired conditions may not be maintained in a single cylinder.
It is, therefore, a still further object of this invention to provide a fuel injection control for a direct cylinder injected two cycle engine having multiple cylinders wherein the injection control is based on effects caused by cylinders other than that in which the fuel is being injected.